Conductor strip formed with slit, cutout or grooves

ABSTRACT

A conductor strip includes a first end portion soldered to a printed circuit board, and a second end portion welded to a rechargeable battery. The conductor strip also includes a connecting portion disposed between the first and the second end portions. The connecting portion has a smaller width than that of the first end portion so that the peeling force acting on the first end portion is alleviated.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a conductor strip used formaking an electrical connection between a printed circuit and a battery.It also relates to a connecting arrangement of such a conductor stripand a circuit board.

[0003] 2. Description of the Related Art

[0004] Recently portable electronic devices including notebookcomputers, cell phones, etc., have been widely used because of theirhandiness. For enabling outside use, the cell phone for example operateson a rechargeable battery housed in a battery pack together with othernecessary components. The battery pack, readily detachable for exchangeof the battery, includes a battery cell and a protection unit connectedto the cell for preventing the cell from over-discharging or beingovercharged.

[0005]FIG. 16 shows some aspects of a conventional protection unit U₀ ofthe above type. As illustrated, the conventional unit U₀, used for arechargeable battery cell 100, includes a printed circuit board 200,electronic components 300 mounted on the board 200, and two conductorstrips 400 connected to the battery cell 100. Each of the conductorstrips 400 includes a rectangular connecting portion 400 a and anotherrectangular connecting portion 400 b. The first connecting portion 400 ais soldered to a pad (not shown) provided on the board 200, while thesecond connecting portion 400 b is welded to the cathode or anode (notshown) of the cell 100. The conductor strip 400 is bent so that thesecond connecting portion 400 b is perpendicular to the first connectingportion 400 a.

[0006] While the conventional conductor strip 400 has a simpleconfiguration and thus can be made easily, it entails the followingdrawbacks.

[0007] As seen from FIG. 16, the first connecting portion 400 a of theconventional strip 400 does not have any holes or gaps in it. Thus, itis impossible to observe the bonding condition of the solder after theapplied solder hardens between the connecting portion 400 a and theboard 200. Another problem is that the conductor strip 400 is detachedfrom the board 200 rather easily, due to its simple structure, uponexertion of an upward force on the second portion 400 b.

SUMMARY OF THE INVENTION

[0008] The present invention has been proposed under the circumstancesdescribed above. It is, therefore, an object of the present invention toprovide a conductor strip that can be firmly attached to a printedcircuit board and also permits easy inspection of the solder-bondingcondition.

[0009] According to a first aspect of the present invention, there isprovided a conductor strip comprising: a first end portion fixed to afirst member; a second end portion fixed to a second member; and aconnector arranged between the first end portion and the second endportion. The connector is smaller in size than the first end portion ina width direction perpendicular to another direction connecting thefirst end portion and the second end portion.

[0010] Preferably, the connector may extend from a central part of thefirst end portion.

[0011] Preferably, the conductor strip may further comprise a projectiondisposed adjacent to the connector, wherein the projection extends fromthe first end portion toward the second end portion.

[0012] Preferably, the connector may comprise two connecting portionsspaced from each other in the width direction.

[0013] Preferably, a U-shaped slit may be formed in the conductor strip.

[0014] Preferably, the first end portion may be soldered to the firstmember. The second end portion may be welded to the second member.

[0015] According to a second aspect of the present invention, there isprovided a conductor strip that comprises: a first end portion fixed toa first member; and a second end portion fixed to a second member. Thefirst end portion is formed with a plurality of grooves for improvingthe bonding strength of solder material applied between the first endportion and the first member.

[0016] Preferably, each of the grooves may have a triangular crosssection.

[0017] Preferably, the plurality of grooves may comprise grooves thatperpendicularly intersect each other.

[0018] According to a third aspect of the present invention, there isprovided an assembly that comprises: a conductor strip that includes afirst end portion, a second end portion, and a connector disposedbetween the first and the second end portions; and a substrate thatsupports the conductor strip. The connector is smaller in width than thefirst end portion.

[0019] Preferably, the connector may at least partially project from thesubstrate.

[0020] According to a fourth aspect of the present invention, there isprovided a method of soldering a conductor strip to a supporting member,wherein the conductor strip is formed with a U-shaped slit. The methodcomprises the steps of: applying solder paste to the supporting memberin a manner such that a solder-void region is formed on the supportingmember; positioning the conductor strip on the supporting member; andmelting the applied solder paste. The conductor strip is positioned onthe supporting member so that the U-shaped slit exposes the solder-voidregion.

[0021] Other features and advantages of the present invention willbecome apparent from the detailed description given below with referenceto the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0022]FIG. 1A is a perspective view showing the principal features of abattery pack incorporating conductor strips provided by the presentinvention;

[0023]FIG. 1B is a plan view showing the principal part of the conductorstrip of the present invention;

[0024] FIGS. 2A˜2C illustrate how the conductor strip of the presentinvention is soldered to a pad;

[0025]FIG. 3 is the graph showing the relation between the peel strengthand the distance of pull regarding a conventional conductor strip andthe conductor strip of the present invention;

[0026]FIG. 4A illustrates how the conductor strip of the presentinvention can be stably attached to the substrate;

[0027]FIG. 4B illustrates how the conventional conductor strip is peeledoff the substrate upon application of an upward external force;

[0028]FIG. 5 shows a possible way to fix the conductor strip of thepresent invention to the substrate;

[0029]FIGS. 6 and 7 are a plan view showing a possible configuration ofthe slit formed in the conductor strip of the present invention;

[0030] FIGS. 8A˜8C are plan views showing how the conductor strip of acutout-type can be mounted on the substrate;

[0031]FIG. 9 illustrates the advantageous feature of the cutout-typeconductor strip;

[0032]FIGS. 10 and 11A˜11B are plan views showing other possibleconfigurations of the cutout-type conductor strip;

[0033]FIG. 12 illustrates the advantageous feature of the conductorstrip shown in FIGS. 11A˜11B;

[0034] FIGS. 13A˜13B illustrate a groove-type conductor strip of thepresent invention;

[0035]FIG. 14 illustrates the advantageous feature of the groove-typeconductor strip;

[0036]FIG. 15 shows a possible modification of the groove-type conductorstrip; and

[0037]FIG. 16 shows the principal features of a conventional batterypack.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0038] Preferred embodiments of the present invention will be describedbelow with reference to the accompanying drawings. Throughout thesefigures, similar or identical elements are indicated by the samereference signs.

[0039]FIG. 1A shows the principal components of a battery pack utilizingconductor strips provided by the present invention. The battery pack maybe used as a power source for a cell phone, notebook computer, etc. Asillustrated, the battery pack includes a rechargeable battery cell 1 anda protection unit U1. The cell 1 has a side surface 1 a in which acathode and an anode (not shown) are provided. The protection unit U1 isconnected to the cell 1 for preventing the cell 1 from over-dischargingor being overcharged. The unit U1 includes an insulating substrate 2,pads 3 formed on the substrate 2, electronic devices 4 mounted on thesubstrate 2, and two conductor strips 5.

[0040] The substrate 2, made of e.g. a glass-fabric-based epoxy resin,has an upper surface 2 a upon which a wiring pattern (not shown) isformed of cupper. The wiring pattern is connected to the electronicdevices 4 and the pads 3. Each of the conductor strips 5 has a firstterminal 5 a connected to the pad 3 and a second terminal 5 b connectedto the cathode or anode of the battery cell 1. The strip 5 may initiallybe flat as a whole, but be bent to be connected to the cell 1, as shownin FIG. 1A.

[0041] In the illustrated embodiment, a staple-shaped (U-shaped) slit 6(K=0.4 mm) is formed in the first terminal 5 a of each strip 5, wherebythe strip 5 is provided, as shown in FIG. 1B, with two connectingportions 5 c and a rectangular projection 5 d (H=0.5 mm) disposedbetween the connecting portions 5 c. The width W₁ of each connectingportion 5 c is smaller than the width W₂ (=2.5 mm) of the conductorstrip 5. The technical significances of the slit 6 will be describedlater.

[0042] The first terminal 5 a of each strip 5 is soldered to the pad 3in the following manner. First, as shown in FIG. 2A, solder paste isapplied to the pad 3 to form a narrow paste land (first land) 7 a and alarger, rectangular paste land (second land) 7 b spaced from the firstland 7 a by a prescribed short distance. A linear region 8 is betweenthe two lands 7 a and 7 b, which is left uncovered by the solder paste.The application of the solder paste may be performed by using a maskformed with openings corresponding to the first and the second lands 7a, 7 b. The mask is laid on the pad 3, and then solder paste is spreadover the mask with a squeegee.

[0043] As shown in FIG. 2B, the conductor strip 5 is placed on the pad 3so that a part of the solder-void region 8 is observed through the slit6. The strip 5 may be automatically set into place with the use of asuction collet. Then, the substrate 2 together with the strips 5 (the“strip-substrate assembly” below) is heated in a furnace to melt theapplied solder paste 7. The molten solder material is spread over thepad 3 under the weight of the conductive strip 5. Then, thestrip-substrate assembly is taken out of the furnace to allow the soldermaterial to cool. Subsequently, the solder solidifies, to secure thestrip 5 to the pad 3.

[0044] For fixing the strip 5 to the pad 3 properly, the molten solderneeds to be spread uniformly between the first terminal 5 a and the pad3. When this ideal condition is attained, the first terminal 5 a as awhole will be fixed to the pad 3 after the strip-substrate assembly isbrought out from the furnace.

[0045] Advantageously, the slit 6 formed in the first terminal 5 aenables ready inspection of whether the soldering has been performedproperly or not. Specifically, when the molten solder is spreaduniformly between the first terminal 5 a and the pad 3, the linearregion 8 will disappear. When the solder has failed to be spreadproperly, on the other hand, the linear region 8 will remain partiallyor entirely. In the illustrate embodiment, the remaining or disappearingof the region 8 can be simply observed through the slit 6.

[0046] In addition to the above advantage, the slit 6 contributes to theimprovement in peel strength of the conductor strip 5. Referring to FIG.3, the graph shows the relation between the ‘peel strength’ and the‘distance of pull’ (“PS-DP relation” below) with respect to theconventional strip 400 (FIG. 16) and the strip 5 of the presentinvention. The ‘distance of pull’ indicates how much the second terminal5 b or 400 b is pulled upward (see FIGS. 4A and 4B). The graph of FIG. 3shows that the maximum peel strength Cmax of the conventional strip 400is about 20 N(newton), whereas the maximum peel strength Pmax of thestrip 5 of the present invention is nearly 40 N. The reason why the peelstrength Pmax of the strip 5 is greater than the peel strength Cmax ofthe conventional strip 400 is as follows. As seen from FIG. 16, thefirst terminal 400 a of the conventional strip 400 is a simplerectangular plate provided with no countermeasure to resist the peelingforce. Thus, as the graph of FIG. 3 shows, the peel strength of theconventional strip is relatively low after the maximum peel strengthCmax is attained.

[0047] The strip 5 of the present invention exhibits generally the same“PS-DP relation” as that of the conventional strip 400 when the distanceof pull is about 0˜0.6 mm (see FIG. 3). Then, when the distance of pullis about 0.6˜1.6 mm (the range Sw in FIG. 3), the strip 5 is peeled offthe substrate more easily than the conventional strip 400. The strip 5exhibits the weaker peel strength because the peeling is proceeding withrespect to the relatively narrow connecting portions 5 c. Thereafter,the peel strength of the strip 5 becomes greater than that of theconventional strip 400. This is because the projection 5 d of the strip5 clings to the substrate 2, as shown in FIG. 4A, thereby serving as anadditional resisting portion against the peeling force F.

[0048] In the above-described embodiment, the strip 5 is supported bythe substrate 2 so that the slit 6 as a whole is located on thesubstrate 2. The present invention is not limited to this, and the slit6 may partially be off the substrate 2, as shown in FIG. 5. Further, thestrip 6 may not have the staple-like, angular configuration, but have asmooth, arcuate (U-shaped) form, as shown in FIG. 6. Still further, theconductor strip 5 may be formed with two slits 6, as shown in FIG. 7. Inthe illustrated example, each of the two end portions of the strip 5 isformed with one slit 6 and connected to a substrate 2 or 2′.

[0049]FIG. 8A shows another possible configuration of the strip 5. Inthis embodiment, the first terminal 5 a is formed with two rectangularcutouts spaced across a relatively narrow connecting portion 5 c. Withsuch an arrangement again, the remaining or disappearing of the linearregion 8 (FIG. 2A) is observed through the rectangular cutouts. Thus,the quality inspection of the reflow soldering is readily performed. Inthe illustrated example, d₁ may be 3.0 mm, d₂ may be 3.0 mm, and d₃ maybe 0.25˜0.75 mm.

[0050] If the above inspection is not required, the strip 5 may bepositioned so that the connecting portion 5 c projects from the edge ofthe substrate 2 entirely as shown in FIG. 8B or partially as shown inFIG. 8C. The position of FIG. 8C is more advantageous to performingself-alignment of the strip 5 than that of FIG. 8, since the moltensolder 7 can enclose the connecting portion of the strip 5 morethoroughly.

[0051] Like the slit-forming arrangement described above, thecutout-forming arrangements of FIGS. 8A˜8C contribute to the improvementof the peel strength of the strip 5. Referring to FIG. 9, when an upwardexternal force F is exerted on the second terminal 5 b, the firstterminal 5 a is about to be pulled upward. Differing from the prior artcase (FIG. 16), the effect of the pulling force acts on the firstterminal 5 a via the relatively narrow connecting portion 5 c. As aresult, part of the external force F may be directed in the normaldirection to the substrate surface 2 a, which is the most effectivedirection for peeling off the first terminal 5 a, while the other partof the external force F will act in slant directions to the substratesurface 2 a, which are less effective peeling-off directions.Consequently, a greater external force is required to peel off the strip5 than in the case of the conventional strip 400. The cutout formed inthe strip 5 may be semi-circular, as shown in FIG. 10.

[0052] According to the present invention, the first terminal 5 a of thestrip 5 shown in FIG. 8A may be provided with two protrusions 5 e thatextend from the first terminal 5 a toward the second terminal 5 b, asshown in FIG. 11A. With such an arrangement, the first terminal 5 a iskept attached to the pad 3 more firmly than when only the narrowconnecting portion 5 c is provided between the first and the secondterminals 5 a, 5 b. The reason is as follows. Referring to FIG. 12, whenthe upward external force F acts on the second terminal 5 b, the pullingforce is transmitted to the first terminal 5 a via the narrowerconnecting portion 5 c. Thus, as in the case described with reference toFIG. 9, the first terminal 5 a is attached to the pad 3 more stronglythan is conventionally possible. Further, according to the arrangementof FIG. 12, the projections 5 e remain to be attached to the substrate 2even after the connecting portion 5 c is peeled off. Accordingly, thebinding strength between the first terminal 5 a and the substrate 2 isrendered much stronger. As shown in FIG. 11B, the connecting portion 5 cmay partially protrude from the edge of the substrate 2.

[0053] According to another embodiment of the present invention, aplurality of grooves 9 may be formed on the bottom side of the firstterminal 5 a of each conductor strip 5, as shown in FIGS. 13A and 13B.In the illustrated example, each groove 9 extends widthways of thestrip. 5 and has a triangular cross section (see FIG. 14). In thisarrangement, the molten solder material 7 fills the grooves 9, as shownin FIG. 14, and then hardens.

[0054] The above groove arrangement is advantageous to achievingreliable fixation of the strip 5 to the substrate 2. The reason is asfollows. Referring to FIG. 14, the triangular configuration of eachgroove 9 is defined by a first slant surface 9 a and a second slantsurface 9 b. When an upward external force F is exerted on the secondterminal 5 b of the strip 5, the second slant surface 9 b of therightmost groove 9 may be peeled off the solder material 7 ratherreadily because the peeling force f₁ acts in a direction generallyperpendicular to the second slant surface 9 b. After the second surface9 b is detached, a peeling force f2 is exerted on the first slantsurface 9 a. The acting direction of this force, however, is generallyparallel to the first slant surface 9 a, as seen from FIG. 14. Since thebonding force of the solder 7 is strong in this direction, the firstterminal 5 a can remain to be attached to the substrate 2 against agreat external force.

[0055] As shown in FIG. 15, the conductor strip 5 may additionally beformed with a plurality of grooves 10 extending longitudinally of thestrip 5. With such an arrangement, the strip 5 can remain to be attachedto the substrate 2 upon application of a rather great torsional force f₃about the longitudinal axis La.

[0056] According to the present invention, the grooves 9 may not bestraight or have a triangular cross section.

[0057] The grooves 9 and/or 10 may be formed in the conductor stripshown in FIGS. 1A, 6, 7, 8A˜8C, 10 or 11A˜11B.

[0058] The present invention being thus described, it is obvious thatthe same may be varied in many ways. Such variations are not to beregarded as a departure from the spirit and scope of the presentinvention, and all such modifications as would be obvious to thoseskilled in the art are intended to be included within the scope of thefollowing claims.

1. A conductor strip comprising: a first end portion fixed to a first member; a second end portion fixed to a second member; and a connector arranged between the first end portion and the second end portion; wherein the connector is smaller in size than the first end portion in a width direction perpendicular to another direction connecting the first end portion and the second end portion.
 2. The conductor strip according to claim 1, wherein the connector extends from a central part of the first end portion.
 3. The conductor strip according to claim 1, further comprising a projection disposed adjacent to the connector, wherein the projection extends from the first end portion toward the second end portion.
 4. The conductor strip according to claim 1, wherein the connector comprises two connecting portions spaced from each other in the width direction.
 5. The conductor strip according to claim 1, further comprising a U-shaped slit.
 6. The conductor strip according to claim 1, wherein the first end portion is soldered to said first member.
 7. A conductor strip comprising: a first end portion fixed to a first member; and a second end portion fixed to a second member; wherein the first end portion is formed with a plurality of grooves.
 8. The conductor strip according to claim 7, wherein each of the grooves has a triangular cross section.
 9. The conductor strip according to claim 7, wherein the plurality of grooves comprise grooves that perpendicularly intersect each other.
 10. An assembly comprising: a conductor strip that includes a first end portion, a second end portion, and a connector disposed between the first and the second end portions; and a substrate that supports the conductor strip; wherein the connector is smaller in width than the first end portion.
 11. The assembly according to claim 10, wherein the connector at least partially projects from the substrate.
 12. A method of soldering a conductor strip to a supporting member, the conductor strip being formed with a U-shaped slit, the method comprising the steps of: applying solder paste to the supporting member in a manner such that a solder-void region is formed on the supporting member; positioning the conductor strip on the supporting member; and melting the applied solder paste; wherein the conductor strip is positioned on the supporting member so that the U-shaped slit exposes the solder-void region. 